Most conventional magnetic recording media are the coated type which is produced by dispersing particles of magnetic oxides or ferromagnetic alloys such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a Berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 and CrO.sub.2 in an organic binder such as a vinyl chloride/vinyl acetate copolymer, a styrene/butadiene copolymer, an epoxy resin or polyurethane resin. The resulting coating solution is applied to a non-magnetic base, followed by drying the coating. However, due to the recent increasing demand for higher density recording, researchers' attention has been drawn to magnetic recording media of thin metal film type that uses as a magnetic recording layer a thin ferromagnetic metal film that is formed by the vapor deposition such as vacuum vapor deposition, sputtering or ion plating, or the plating such as electroplating or electroless plating. Various efforts are being made to use such recording medium on a commercial scale.
Most of the magnetic recording media of the coated type use a metal oxide with small saturation magnetization as a magnetic material. Therefore, an attempt to achieve high-density recording by using a thinner magnetic recording medium results in a decreased signal output. By using a magnetic recording medium of thin metal film type, a very thin magnetic recording layer can be formed by applying a ferromagnetic metal having a greater saturation magnetization than that of the magnetic oxide without using a non-magnetic material such as binder. This thinness is very advantageous for providing good electro-to-magnetic conversion characteristics. However, the thin metal film type magnetic recording medium has its own problems: (1) it develops friction against the magnetic head, guide poles or other transport means when it is run to record, reproduce or erase magnetic signals, and hence wears easily; (2) it is easily attacked by corrosive environments; and (3) the magnetic recording layer may be damaged by impacts during handling.
Some attempts have been made to solve these problems by forming a protective layer on the magnetic recording medium of the thin metal film type. One such proposal is described in Japanese Patent Application (OPI) No. 75001/75 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") wherein a thin lubricant layer is formed on the metal film. According to this proposal, the coefficient of friction between the magnetic head or guide poles and the metal film is reduced to provide a tape that runs consistently and which is the least likely to be abraded. However, these advantages are quickly lost if the tape is used repeatedly. Another method is described in Japanese Patent Application (OPI) Nos. 39708/78 and 40505/78 wherein a lubricant protective layer made of a metal or metal oxide is formed on the thin metal film, but even in this case, the effect of the protective layer does not last long and as the tape is used repeatedly, the friction coefficient increases rapidly or the thin magnetic metal film breaks. Still another method is described in Japanese Patent Application (OPI) No. 155010/79 wherein an overcoat of a high molecular film is formed on the metal film. However, if the overcoat is made of vinylidene chloride/acrylic ester copolymer and other known high molecular substances, the resulting film thickness is at least about 0.2.mu. and this causes spacing loss which in turn leads to reduced output in high density recording.
To achieve high density recording, most thin magnetic metal films are supported on a very smooth base. However, regardless of how smooth the base surface is, none of the lubricating methods described above can provide a magnetic recording medium having good running properties, especially in very humid atmospheres, or high wear resistance.